A stateless person is someone with no state nor nationality. It may be because the state that gave their previous nationality has ceased to exist and there is no successor state, or their nationality has been repudiated by their own state, making them effective refugees. People may also be stateless if they are members of a minority ethnic group which is denied citizen status in the country on whose territory they are born, if they are born in disputed territories, if they are born in an area ruled by an entity whose independence is not internationally recognized, or if they are born on territory over which no modern state claims sovereignty. Individuals may also become stateless voluntarily, by formally renouncing their citizenship while on foreign soil; however, not all states recognize such renunciations on the part of their citizens.

Some areas, such as the Palestinian Territories, are under military occupation by a country which does not issue passports to its residents. In some cases, such as that of ethnic Russians in Latvia, conditions for citizenship may be problematic or difficult to satisfy. In some enclave areas, such as the FARC-ruled areas of Colombia, and parts of Sudan and Afghanistan, people may have no practical contact with a potentially passport-issuing state which nominally claims sovereignty over them.

While stateless persons were more common before the 20th century, when states were somewhat more fragile entities, on September 20, 1954 the United Nations adopted the Convention relating to the Status of Stateless Persons: an active policy to prevent people becoming or remaining stateless. States which have ratified the Convention are bound to give stateless persons rights similar to those granted aliens of comparable status. Despite this, there are still Kashmiri, Kurdish, Palestinian and Sahrawi refugees who claim asylum due to statelessness, for example.

Cases of de facto statelessness have arisen due to historical provisions of British nationality law which led to cases where people have had a British passport without Right of abode in the United Kingdom. Those with such status who did not have citizenship or residence rights in any other country were effectively stateless despite holding British nationality. Effective 30 April 2003, as part of the Nationality, Immigration and Asylum Act 2002 the United Kingdom gave most British nationals without any other citizenship the right to register as full British citizens if they wish and has hence resolved most of the British cases of effective statelessness. A similar case can be seen in illegal aliens who can't be expelled due to specific provisions (health issues, stateless persons who by definition can't be expelled to their "original country", refugees who are not accepted by their original state, etc.): they thus live in a judicial no man's land.

A slightly tragicomic rendition of this condition was portrayed in the motion picture The Terminal, in which a man is trapped living inside an airport because he cannot return home due to his unrecognized citizenship status (his homeland has collapsed while he is in transit). This story was based in part on the real-life story of Merhan Karimi Nasseri, who spent several years in the Charles de Gaulle Airport due to conflicts with French law and the fact he was not welcome in his country of origin.